Electron beam powder bed fusion (PBF-EB) is a known metal additive manufacturing (AM) technology. Processing non-conducting powders such as ceramics has so far been considered as not feasible because of the inherent problems with Coulomb repulsion due to insufficient electrical conductivity. In this study, a method for functionalizing ceramic powder is proposed where particles are electroless coated by a ~ 1 µm Ni layer to decrease the surface resistivity. The feasibility of the suggested approach is tested on Al₂O₃ powder, and the results show that the coated ceramic powder has a decreased surface resistivity, which enables processing by PBF-EB. Heating and melting parameters were investigated and samples were manufactured at ~ 1600 °C. Sintered and melted powders were analyzed by microscopy and micromechanically tested by nanoindentation. Calculations, visual observation and SEM–EDX suggest that the Ni coating is evaporated during the process, which suggests that the process could be feasible for the manufacturing of pure ceramic parts.

Materials for components installed in the hot section of gas turbines must endure highly aggressive conditions, such as elevated temperatures and corrosive environments. Under these scenarios, CVD mullite coatings enriched in alumina in the outer surface have demonstrated excellent thermal stability and protection to SiC against corrosion and recession. It is essential that, in addition to the excellent protective behavior exhibited by Al-rich mullite coatings, their structural integrity and mechanical properties can be retained after their exposure to such aggressive conditions. This investigation is devoted to the study of the effect of temperature and hotcorrosion on the main micro-nanomechanical properties and performance of mullite-based EBCs. Nanoindentation was conducted to determine coatings' hardness, stiffness and fracture toughness whereas nanoscratch tests allowed evaluating their intrinsic structural integrity. Temperature and corrosion were found to have a minor effect on the mechanical behavior of the studied coatings. Hardness and Young's modulus remained comparable after thermal treatments, and scratch tests show similar damage features. From these results it can be concluded that mullite-based coatings present a satisfactory structural integrity and reliability to be used as environmental barrier coatings for hot environments. (C) 2014 Elsevier Ltd. All rights reserved.Postprint (author’s final draft

In this work, a highly alloyed cold work tool steel, Uddeholm Vanadis 4 Extra, was manufactured via the electron beam melting (EBM) technique. The corresponding material microstructure and carbide precipitation behavior as well as the microstructural changes after heat treatment were characterized, and key mechanical properties were investigated. In the as-built condition, the microstructure consists of a discontinuous network of very fine primary Mo- and V-rich carbides dispersed in an auto-tempered martensite matrix together with ≈15% of retained austenite. Adjusted heat treatment procedures allowed optimizing the microstructure by the elimination of Mo-rich carbides and the precipitation of fine and different sized V-rich carbides, along with a decrease in the retained austenite content below 2%. Hardness response, compressive strength, and abrasive wear properties of the EBM-manufactured material are similar or superior to its as-HIP forged counterparts manufactured using traditional powder metallurgy route. In the material as built by EBM, an impact toughness of 16–17 J was achieved. Hot isostatic pressing (HIP) was applied in order to further increase ductility and to investigate its impact upon the microstructure and properties of the material. After HIPing with optimized protocols, the ductility increased over 20 J.

Highly ordered TiO₂ nanotubes were obtained by anodization on Ti6Al4V substrates manufactured by electron beam powder bed fusion (E-PBF). Effects of anodization parameters such as anodizing time, stirring, fluoride concentration, and water content were analyzed in an organic electrolyte (ethylene glycol) that contains ammonium fluoride. The ordering of the nanotubes was measured by regularity ratio calculations based on fast Fourier transform (FFT) from SEM images. It was found that for the processed specimens, the highest ordering of the TiO₂ nanotubes was reached at 30 V for 5000 s with a concentration of 9 vol% H₂O and 0.4 wt.% NH₄F, exhibiting nanotubes free of delamination, cracks, and coral-like structures with a regularity ratio (RR) of 1.91. This work offers a simple method for creating homogeneous and organized TiO₂ nanotubes on Ti6Al4V substrates manufactured by E-PBF which potentially improves its functionality in diverse industrial applications such as nanosensors, controlled-release substances, solar cells, water splitting, electrochromic devices, and Li-ion battery anodes. Graphical Abstract

In this study, the structural integrity of mullite (3Al₂O₃·2SiO₂) films, deposited on silicon carbide (SiC) substrates using chemical vapor deposition (CVD), was investigated via increasing load nanoscratch tests. The films were configured by mullite columns of stoichiometric composition growing from a silica-rich layer in contact with the SiC substrate. Controlled damage was induced in the 3Al₂O₃·2SiO₂ films at relatively low scratch loads. Radial and lateral cracking were applied until final delamination and repeated chipping were achieved as the load increased. The intrinsic integrity of the 3Al₂O₃∙2SiO₂ film and the performance of the coated 3Al₂O₃·2SiO₂/SiC system, regarded as a structural unit, were analyzed. With the aid of advanced characterization techniques at the surface and subsurface levels, the configuration and morphology of the damage induced in the coated system by the nanoscratch tests were characterized, and the scratch damage micromechanisms were identified. Finally, the adhesion of the film, in terms of energy of adhesion and interfacial fracture toughness, was determined using different models proposed in the literature. The results from this investigation contribute to the understanding of the mechanical performance and structural integrity of EBC/SiC-based systems, which over the past few years have increasingly been implemented in novel applications for gas turbines and aircraft engines.